CVE-2021-3317 in Server
Summary
by MITRE • 01/27/2021
KLog Server through 2.4.1 allows authenticated command injection. async.php calls shell_exec() on the original value of the source parameter.
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Analysis
by VulDB Data Team • 12/21/2024
The vulnerability identified as CVE-2021-3317 affects KLog Server versions through 2.4.1 and represents a critical command injection flaw that can be exploited by authenticated attackers. This vulnerability resides in the asynchronous processing functionality of the server software, specifically within the async.php script which handles various background operations. The flaw manifests when the system processes user-supplied input through the source parameter without proper sanitization or validation, creating an environment where malicious commands can be executed with the privileges of the web server process.
The technical implementation of this vulnerability stems from the insecure use of shell_exec() function in the async.php file. When an authenticated user submits a request containing a malicious source parameter value, the application directly passes this input to shell_exec() without any input validation or sanitization measures. This primitive approach to command execution creates a direct pathway for arbitrary code execution on the server, as the shell_exec() function interprets the input as shell commands rather than data. The vulnerability is classified under CWE-78 as a "Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')" which is a well-documented and dangerous class of vulnerabilities that can lead to complete system compromise.
The operational impact of this vulnerability extends far beyond simple data theft or service disruption. An authenticated attacker with access to the system can leverage this command injection to execute arbitrary commands on the underlying operating system, potentially gaining full control over the server. This includes the ability to read sensitive files, modify system configurations, install malware, or establish persistence mechanisms. The vulnerability affects not only the immediate server environment but can also serve as a stepping stone for further lateral movement within network infrastructures, particularly in environments where KLog Server is used for network monitoring or security operations. The authentication requirement does not significantly mitigate the risk as it only requires legitimate access to the system, which could be obtained through credential compromise or other means.
Mitigation strategies for CVE-2021-3317 should focus on immediate patching of the affected KLog Server versions, with the vendor releasing updates that address the improper input handling in async.php. Organizations should implement proper input validation and sanitization mechanisms that prevent shell metacharacters from being processed as commands. The use of parameterized commands or secure alternative functions that do not invoke shell execution should be implemented. Additionally, network segmentation and privilege separation can help limit the potential impact of exploitation. Security monitoring should be enhanced to detect unusual command execution patterns, and access controls should be reviewed to ensure that only necessary users have authenticated access to the vulnerable functionality. This vulnerability aligns with ATT&CK technique T1059.001 for Command and Scripting Interpreter, specifically focusing on the execution of system commands through shell interfaces. Organizations should also consider implementing web application firewalls and input filtering mechanisms to detect and block malicious payloads targeting this specific command injection vector.